The broad goals of this project are: 1) to define neural systems underlying selective attention and discrimination in monkeys; 2) to develop a direct link between the disparate neurophysiologic approaches to this issue in monkeys and humans. The human - simian link is based on using spatial and feature attention tasks directly adapted from human studies and on using depth recording techniques that integrate a "neural systems" level of analysis with the specificity of single cell recording, and yet, are directly comparable to visual event related potential (ERP) recording in humans. Brain electrical source analysis (BESA) of surface ERP will provide hypotheses concerning the spatiotemporal pattern of attentional modulation of sensory processing throughout the brain as well as the involvement of particular structures in task-specific effects, and in generating the surface ERP distribution. In-vivo MRI will be used to transpose BESA-derived source configurations onto brain structures and will help in targeting structures for depth studies. Depth recordings will provide both an unparalleled direct means of evaluating and extending the predictive capacity of BESA, and a powerful, independent approach to studying attentional modulation of sensory processes. Depth studies use three complementary methods. Recording of the ERP depth profile allows tracing of ERP components from the brain's surface to their depths of maximum amplitude and polarity inversion. With penetrations normal to a structures lamination pattern, one/dimensional current source density (CSD) analysis of the ERP profile delineates the spatiotemporal pattern of transmembrane current flow which is elicited by visual stimuli and which generates the distribution of field potentials (ERP) in the extracellular medium. Recording of the profile of multiunit activity (MUA), concomitant to the ERP, helps to interpret features in the CSD profile (current sources and sinks) as indices of excitatory and inhibitory postsynaptic potentials, and to link these data to those of approaches measuring action potentials alone. Recording these profiles from numerous incremental depths simultaneously with multicontact electrodes yields a sensitive and reliable measure of the real-time sequence and quantitative distribution of activity over the entire depth of a visual structure. Relating these data to known distributions of cell type and connectivity can evaluate the physiology of structures less than 100 mum thick, and can help to identify the neural basis for surface ERP components. Data will be collected from cortical and subcortical structures in the "form and color" parvocellular- inferotemporal, nd "space and movement" magnocellular-parietal pathways in awake monkeys during performance of visual spatial and feature attention tasks. The specific aims are: 1) To delineate the functional neuroanatomy of attention effects in the visual pathways; 2) to define neurophysiologic processes underlying attentional modulation of sensory processes; 3) to examine the dynamics of attention effects, as governed by discriminative difficulty and discriminandum complexity, emphasizing the earliest stages of effect and the timing of activity within and across structures. The studies will supplement the fundamental understanding of sensory processing in the primate. Defining aspects of processing reflected in the surface- ERP will increase our understanding of both normal and pathological visual function in humans.